In general we talk about to the horizon. But many signals do not make it that far, but sometimes during the summer when atmospheric conditions permit, then distances can be many times that normal range. But propagation is not normally an all day every day effect. In general, things like buildings, vehicles, trees, land rises etc etc all attenuate a signal. Thus height is one of the biggest factors under normal band conditions when it comes to distance. The higher one of the antennas is the further the distance will be, as there is less to get in the way. The higher both the antennas are, the better it gets again, as nothing but fresh air & the earth curvature will be in the way. Range within a built up area handheld to handheld under normal conditions will be a few hundred meters at the most. In wooded areas, especially when the trees have leaves on them, expect VERY VERY short range & if you ever see the kilometres that these licence free 446 radios suggest as thier range, then that will be mountain top to mountain top, with nothing in between the antennas but fresh air & even then, that is on a good day, not what you can expect every time.Another factor is the antenna in use. Is it designed for the frequency in use? And that is not, does it work on that frequency? But is the antenna designed to be optimised & efficient on that frequency? As scanner listeners, we use compromise antennas. No antenna is efficient across more than a couple of Megahertz & size & height at which the antenna is mounted also matters. As does the coax used to connect the antenna to the radio.Some of the biggest lies in radio are made about antennas & how well they work. This so called gain in an antenna, is about about how much better it works than a half wave,)two part) dipole. That is an antenna with a radiator & a counter balance, (counterpoise.) And that second half of any antenna is VERY important. Some antennas work reasonably well without that counterpoise, but in general all antennas work better with that second half.Cheap & nasty coax will easily loose 50% of the signal & much more than that, even at around 10 meters in length. The path the signal travels is also important. Sometimes just moving a antenna a few feet can be the difference between a building, or a tree etc being in the way & the signal being very strong or non existent. So how far does a signal travel? If you can tell us the exact location of each transmission, the heights & antenna types in use, how much power is in use & what the propagation conditions were like we can start to make an educated guess.

Thanks for replys!The frequency is 165.6900.Conversation.London eye,London Bridge,this is Bankside,any one hear me?Westminster to London Eye,yes this is Canary Wharf.There is more general conversation.Watson WSMA-881 aerial on Uniden scanner.Heard Saturday am.

As you mention several Thamesside locations, it could well be any one of the myriad of tourist boats etc. There are several sites along the Thames, including Greenwich from which these transmissions could originate.

I found one such service many moths ago and was able to confirm by listening out for clues (routes, names of vessels etc and doing Google searches).

165.69 is not an exact frequency.It will either be 169.6875 or 169.7, or possibly 165.69375.Or it's not the real freq, and you are detecting the ghost of another strong nearby signal.There is nothing on those freqs in central London according the OFCOM Spectrum Information Portal (though not unusual for it to be out of date)Is this NFM analog? any CTCSS/DCS?

I reserve the right to ignore people who have made no attempt to the read the manual, and expect others to do it for them.

Another possibility is that it was something temporary associated withe cycle race in London yesterday. They were using three airborne repeaters around 452 MHz which covered a huge area.But the frequency you state does seem practical for this as it would interfere with other users.

I reserve the right to ignore people who have made no attempt to the read the manual, and expect others to do it for them.